The present invention relates to a programmable device for integrated circuits, and more specifically, to a programmable device operatively connected to an integrated circuit (IC) to provide signal termination or predetermined logic levels to logic elements in the IC.
Certain types of digital logic integrated circuits require termination circuits for satisfactory operation. Proper termination prevents reflections and ringing. For example, emitter coupled logic (ECL) and transistor transistor logic (TTL) drivers are typically terminated by a resistor or resistor network which is connected to a predetermined voltage level. In parallel termination, an IC logic gate is connected to a junction point between two series connected resistors. In diode termination, a pair of inverse parallel diodes serve as the terminating network.
In typical IC board layouts, the required terminating components are provided by single in-line package resistor packs, dual in-line package resistor packs or discrete resistors or diodes. In each case, significant amounts of IC board space are required.
One device for eliminating the need for separate space-consuming circuit terminating packs or discrete elements is disclosed in U.S. Pat. No. 4,811,167 entitled "Integrated Circuit Socket," of which applicant is a co-inventor.
U.S. Pat. No. 4,811,167 discloses an IC socket comprising an insulating member and a plurality of pins for connection to an electrical integrated circuit board. The top of the insulating member includes conductive sockets adapted to be electrically connected to the pins of an IC inserted therein in "piggy-back" fashion. A plurality of impedance elements are provided within the insulating member, and switches are provided on the insulating member for selectively connecting each of the impedance elements to, or isolating each of the impedance elements from a corresponding socket pin.
The IC socket disclosed in U.S. Pat. No. 4,811,167 is highly advantageous in that it eliminates the need for separate space-consuming circuit terminating packs or discrete elements on the IC board. The IC socket is provided beneath the IC and does not require additional board space. However, the use of mechanical switches on the IC socket requires the IC socket to have a higher profile than may be desirable in some applications. Further, in some applications, for example, many military applications, mechanical switches do not meet given specifications and are not acceptable.